lecture 2 animal Flashcards
model organisms are..
easy to study but broadly representative
developmental genes and mechanisms are..
very similar across animal species – fruitflies and humans have similar genes that perform zsimilar functions
studying development in model organisms..
provides knowledge about development IN GENERAL
fertilization
haploid gametes (sperm and egg) join to form a diploid unicellular zygote – that goes through mitosis – multicellular adult will go through meiosis – form gametes – process all over again
fertilization in sea urchins (gametes and cytoplasm inheritence)
sperm and egg are the haploid gametes (egg cytoplasm contains many proteins and organelles involved in early development – offspring’s cytoplasm comes from mother – only thing sperm contributes is nucleic material)
step one sea urchin fertilization
sperm tail, sperm head (within head you have acrosome and nucleus) – acrosome contain digestive enzymes
egg: jelly coat surrounding it – vitelline layer – within have sperm binding receptors – then plasma membrane – within plasma membrane have vacuooles of corticle granules
step two sea urchin fertilization
as sperm connects with the egg – it contacts jelly coat and triggers acrosomal reaction – which is the release of hydrolytic enzymes that digest the jelly coat and try to make way to the receptors.
step three sea urchin fertilization
acrosomal process (thes elong filament things) proteins on the acrosomal process will extend to try to bind to receptors (the proteins are called ligands.)
step four of sea urchin fertilization
plasma membranes fuse together triggering fast block to polyspermy
– once ligand binds, membrane of sperm and membrane of egg fuse. this fusion causes a change in polarity of the egg from slightly negative to slightly positive (depolarization) – this change in polarity pushes away any other sperm trying to come – this process however is short-lived which is why iss called fast block to polyspermy.
step five of sea urchin fertilization
sperm nucleus enters and corticle reaction causes slow block to polyspermy
– once the sperm nucleus enters the egg, the corticle granules are released in between the vitelline layer. these granules will push the vitelline layer away from the plasma membrane of the egg and become the fertilization envelope to keep incoming sperm away – physical separation of the two layers is the slow block to polyspermy
cleavage (sea urchin)
the process by which the zygote becomes multicellular by dividing and dividing – rapid cell division with LITTLE GROWTH (volume doesnt change) of individual cells G1 and G2 skipped.
cleavage results in many smaller cells called (sea urchin)
blastomeres – individual cells getting smaller with each round of division – no growth of cells
in frogs, the zygote becomes a
blastula– hollow ball of cells
blastula
a hollow ball of cells with a fluid filled cavity called the blastocoel– has animal pole and vegetal pole (animal where sperm attached – vegetal pole is opposite where it attached) – cells ar e a bit bigger near vegetal pole
how can cells that possess the same genome look and behave differently
differential gene expression
differential gene expression
– cells express different genes depending on their location and the stagre of development
– expressing different genes leads to the production of different proteins – in turn determines structure and behaviour of cell at given time.
how does a cell know what gwnes to express at any given time - -two mechanisms
–cytoplasmic determinants
- inductive signals
cytoplasmic determinants
the signal to determine if gene is going to be expressed or not comes from within the cell
- molecules within cytoplasm that regulates gene expression – relates to how stuff inside cytoplasm gets distributed to daughter cell – results in different expression (assymetric division – two daughter cells with different contents)
inductive signals
commnication comes from outside of cell (chemical or hormonal) - in vicinity of the cell
– signal molecules cell is exposed to depends on its location within embryo and stage of development – symmetric division +induction (same contents at first but after induction different contents)
what is morphogenesis
the rearrangement of cells or sheets of cells in the embryo – to form different structures
gastrulation
stage where the three germ layers are established and the basic body plan is set up – process of making gut
organogenesis
formation of the organs (neurolation – formation of nervous system (brain..))
what are the three germ layer sthat will be formed
ectoderm, mesoderm, endoderm
ecto = outsider
meso = middle
endo = inner
what will the ectoderm be responsible for
for skin cells – lining of outsidew
what will the mesoderm be responsible for
lining of bones, muscles, connective tissues, blood
what will the endoderm be responsible for
lining of the gut, stomach, intestine..
step 1 frog gastrulation
cells in the vegetal pole push inward – starting at blastopore – invagination move towards the hollow cavity (blastocoel) –
step 2 frog gastrulation
the outer cells (future ectoderm) roll inward, enveloping entirety of embryo blastocoel is getting smaller, and new cavity is being formed (wil be the gut)
step 3 frog gastrulation
blastocoel collapses and new cavity – archenteron is formed – future mesoderm starts extending to form layer
step 4 frog gastrulation
cells at the animal pole spread over outer surface – at the end, little blastopore (anus) is formed
whats the idnication for neurulation
pinching
what are the three ways morphogenesis happens
cells can move positions, change shape, or they can die
convergent extension
example of cells changing their position – produces lionger and narrower structures – without changing number of cells (from 2x3 to 1x6)
changing shape of cell itself step 1
where neural tube is supposed to dform, cells will change their shape. currently they are square with many organelles and microtubules wituin them
changing shape of cell itself step 2
microtubules elongate nice and long
changing shape of cell step 3
actin filaments will get shorter and shorter, creating a pizza slice shaped cell – these shapes will form a curvature along ectoderm
changing shape of cell strep 4
as curveature increases – eventually cells on either end will push towards each other – close of and splits off into a new neural tube (organ)
programmed cell death
fluorescing cells are undergoing apoptosis(cells dying) – removeal of webbing in frogs limbs, to change shape of embryo
